Today, many multimedia devices implement a digital rights management (DRM) framework to allow customers to securely license and download music, movies, and other audio/visual content to such devices. Many multimedia devices support a DRM framework that uses a clock to determine when a multimedia asset expires for a multimedia device. For example, the DRM for a multimedia asset will have a video or music asset expire a week after it is downloaded to a device.
Various pay services are available to deliver content such as movies and music assets to devices such as set-top boxes and personal computers. Different modalities such as a broadcast signal or a network connection may be used to transmit such content to a device of a user. When content is received at the point of a device, such content may be affected by a DRM solution that causes the content to “expire” after a certain period of time. When the content expires, such content cannot be used unless a user updates the DRM license associated with the inactivated content. Such activation may occur via software or by a user calling into a service to request the activation of expired content.
Accordingly, one approach for determining when content expires (in view of a time limit) is to utilize a clock or multiple clocks that is used as a time reference. Such clocks however must be kept secure from tampering in order to properly enforce the DRM protection of an asset. One commonly implemented DRM solution (used by Microsoft) utilizes two clocks where one of the clocks is known as an anti-rollback clock. Such a clock is preset and monitored for tampering, wherein content that uses such a clock as a reference becomes invalidated if such the clock is tampered with. In order to regain access to the inactivated content, a user must obtain a new license to from a content provider or from the operator of a DRM solution to replace that invalidated license, if such invalidation was an accident. There are however significant time and cost concerns to getting a replacement license, because of the difficulty in using software to reset licenses or the element of transacting with an agent over the phone.
There are additional drawbacks to the use of an anti-rollback clock. The clock must be set to be specific time before information used to set such a clock is downloaded. Additionally, relying on a user to properly set the clock can be problematic, especially if the user is lacks a technical background in the use of software or the user sets a clock to the wrong time causing content to become invalidated.
To avoid these problems, some solutions (such as one advocated by Microsoft) recommends the usage of a secure clock where such a clock is set without user intervention and cannot be set by a user. Instead, the secure clock is set via a proxy server via a secured network connection which minimizes the possibility of outside tampering. That is, the connection will fail if the security of the connection is breached. During the connection with a secured clock, a device will then download information to set the internal clock of the device so that content may be used.
Many devices currently use either a secure clock or an anti-rollback clock for DRM solutions that have content that expires. Depending on the type of connection and method of downloading, a player would incorporate one clock system only. That is, if the source of the content is unable to provide a secure clock, the device was relegated to using an anti-rollback solution.
Accordingly, it would be desirable to provide a clock solution where the user is not required to set the clock on the device to match the host clock. Furthermore, it would be preferable to utilize a secure clock in cases where the content provides secure clock support. Finally, it would be desirable to provide multiple clock interfaces that operate transparently from the user's perspective.